Systems and methods for performing spine surgery

ABSTRACT

A method is provided for correcting a curvature or deformity in a patient&#39;s spine based on the digitized locations of implanted screws and tracking the placement of the rod as it is placed in a minimally invasive fashion. The method is implemented by a control unit through a GUI to digitize screw locations, accept one or more correction outputs, and generate one or more rod solution outputs shaped to fit at locations distinct from the implanted screw locations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. patent application claiming the benefit ofpriority from commonly owned and U.S. Provisional Application Ser. No.61/888,990 filed on Oct. 9, 2013 and entitled “Systems and Methods forPerforming Spine Surgery”, the complete disclosure of which is herebyexpressly incorporated by reference into this application as if setforth in its entirety herein.

FIELD

The present application pertains to spine surgery. More particularly,the present application pertains to systems and methods related to theplanning, design, formation, and implantation of spinal implants.

BACKGROUND

The spinal column is a highly complex system of bones and connectivetissues that provide support for the body and protect the delicatespinal cord and nerves. The spinal column includes a series of vertebralbodies stacked atop one another, each vertebral body including an inneror central portion of relatively weak cancellous bone and an outerportion of relatively strong cortical bone. Situated between eachvertebral body is an intervertebral disc that cushions and dampenscompressive forces exerted upon the spinal column. A vertebral canalcontaining the spinal cord is located behind the vertebral bodies. Thespine has a natural curvature (i.e., lordosis in the lumbar and cervicalregions and kyphosis in the thoracic region) such that the endplates ofthe upper and lower vertebrae are inclined towards one another.

There are many types of spinal column disorders including scoliosis(abnormal lateral curvature of the spine), excess kyphosis (abnormalforward curvature of the spine), excess lordosis (abnormal backwardcurvature of the spine), spondylolisthesis (forward displacement of onevertebra over another), and other disorders caused by abnormalities,disease, or trauma (such as ruptured or slipped discs, degenerative discdisease, fractured vertebrae, and the like). Patients that suffer fromsuch conditions often experience extreme and debilitating pain, as wellas diminished nerve function. Posterior fixation for spinal fusions,decompression, deformity, and other reconstructions are performed totreat these patients. The aim of posterior fixation in lumbar, thoracic,and cervical procedures is to stabilize the spinal segments, correctmulti-axis alignment, and aid in optimizing the long-term health of thespinal cord and nerves.

Screws, hooks, and rods are devices used to stabilize the spine during aspinal fixation procedure. Such procedures often require theinstrumentation of many bony elements. The devices, for example rods,can be extremely challenging to design and implant into the patient.Spinal rods are usually formed of stainless steel, titanium, cobaltchrome, or other similarly hard metal, and as such are difficult to bendwithout some sort of leverage-based bender. Moreover, a spinal rod needsto be oriented in six degrees of freedom to compensate for theanatomical structure of a patient's spine as well as the attachmentpoints (screws, hooks) for securing the rod to the vertebrae.Additionally, the physiological problem being treated as well as thephysician's preferences will determine the exact configurationnecessary. Accordingly, the size, length, and particular bends of thespinal rod depends on the size, number, and position of each vertebraeto be constrained, the spatial relationship amongst vertebrae, as wellas the screws and hooks used to hold the rods attached to the vertebrae.

The bending of a spinal rod can be accomplished by a number of methods.The most widely used method is a three-point bender called a FrenchBender. The French bender is a pliers-like device that is manuallyoperated to place one or more bends in a rod. The French bender requiresboth handles to operate and provides leverage based on the length of thehandle. The use of the French bender requires a high degree of physicianskill because the determination of the location, angle, and rotation ofbends is often subjective and can be difficult to correlate to apatient's anatomy. Other methods of bending a rod to fit a screw and/orhook construct include the use of an in-situ rod bender and a keyholebender. However, all of these methods can be subjective, iterative, andare often referred to as an “art.” As such, rod bending and reductionactivities can be a time consuming and potentially frustrating step inthe finalization of a complex and/or long spinal construct. Increasedtime in the operating room to achieve optimum bending can be costly tothe patient and increase the chance of the morbidity. When rod bendingis performed poorly, the rod can preload the construct and increase thechance of failure of the fixation system. The bending and re-bendinginvolved can also promote metal fatigue and the creation of stressrisers in the rod.

Efforts directed to computer-aided design or shaping of spinal rods havebeen largely unsuccessful due to the lack of bending devices as well aslack of understanding of all of the issues involved in bending surgicaldevices. U.S. Pat. No. 7,957,831, issued Jun. 7, 2011 to Isaacs,describes a rod bending system which includes a spatial measurementsub-system with a digitizer to obtain the three dimensional location ofsurgical implants (screws, hooks), software to convert the implantlocations to a series of bend instructions, and a mechanical rod benderused to execute the bend instructions such that the rod will be bentprecisely to custom fit within each of the screws. This is advantageousbecause it provides quantifiable rod bending steps that are customizedto each patient's anatomy enabling surgeons to create custom-fit rods onthe first pass, thereby increasing the speed and efficiency of rodbending, particularly in complex cases. This, in turn, reduces themorbidity and cost associated with such procedures. However, a needstill exists for improved rod bending systems that allow for curvatureand deformity correction in fixation procedures, provide the user withmore rod bending options, and accommodate more of the user's clinicalpreferences including the ability to determine the spatial orientationof the tip of the rod and the tip of the rod pusher relative to oneanother.

SUMMARY

The present invention includes a system and methods for rod bending thatenable the user (e.g., surgeon) to customize screw-based rod bendinstructions to suit the desired correction of a patient's spinalcondition. According to a broad aspect, the present invention includes aspatial tracking system for obtaining the three-dimensional positioninformation of surgical implants, a processing system with software toconvert the implant locations to a series of bend instructions based ona desired correction, and a mechanical rod bender for bending a surgicallinking device to achieve the desired spinal correction.

According to another aspect of the present invention, the spatialtracking system includes an infrared (IR) position sensor and at leastone IR-reflective tracking array attached to a digitizer pointer used todigitize the surgical implant location. The spatial tracking system iscommunicatively linked to the processing system such that the processingsystem may utilize the spatial position information to generate bendinstructions.

According to another aspect of the present invention, the processingsystem is programmed to generate bend instructions based on one or moresurgeon-prescribed clinical objectives. For example, the processingsystem may be programmed to create a custom bend, adjust one or morepoints to which the rod will be bent to, suggest a pre-bent rod option,provide spinal correction in the sagittal plane, provide spinalcorrection in the coronal plane, and provide correction to achieveglobal spinal balance, and as well as perform a plurality ofpredetermined functions. The processing system is further configured topreview and display the results of these clinical objectives and/orpredetermined functions to the user in a meaningful way.

According to another aspect of the invention, the spatial trackingsystem is configured to track the three-dimensional position of a spinalrod relative to the implanted surgical implants during rod insertion.For example, the spatial tracking system may include at least oneIR-reflective tracking array attached to a rod inserter instrument andanother attached to a screw guide rod pusher to continuously digitizethe rod location in real time during insertion of the rod. Theprocessing system is programmed to generate and display the real timethree-dimensional location of the rod tip relative to the tip of the rodpusher and the implanted surgical implants.

According to another aspect of the invention, one or more surgicalprocedures may be performed using various embodiments of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a surgical procedure setup depicting the components of asurgical bending system, according to one embodiment;

FIG. 2 is a perspective view of one embodiment of a digitizer array inthe closed position comprising part of the system of FIG. 1;

FIG. 3 is an exploded perspective view of the digitizer array of FIG. 2;

FIG. 4 is a perspective view of the digitizer array of FIG. 2 in theopen position;

FIG. 5 is a front view of one embodiment of a digitizer pointer assemblycomprising part of the system of FIG. 1;

FIG. 6 is a perspective view of various surgical pointers compatiblewith the digitizer array of FIG. 2;

FIG. 7 is a partial perspective view of the offset pointer of FIG. 6 ina collapsed position;

FIG. 8 is a partial exploded view of the offset pointer of FIG. 6;

FIG. 9 is a partial perspective view of the offset pointer of FIG. 6 inan extended position;

FIG. 10 is a flowchart depicting the steps of the spatial trackingalgorithm according to one embodiment;

FIG. 11 is a flowchart depicting the rod bending workflow according toone embodiment;

FIG. 12 is a flowchart depicting the steps in generating a rod solutionaccording to a first embodiment;

FIG. 13 is a flowchart depicting the steps in generating rod solutionaccording to a second embodiment;

FIG. 14 is a flowchart depicting the steps in generating a rod solutionaccording to a third embodiment;

FIG. 15 is a flowchart depicting the steps of the rod bending processaccording to a first embodiment;

FIG. 16 is a screen shot depicting an example setup screen of the systemof FIG. 1;

FIG. 17 is a screen shot depicting an example IR positioning sensorsetup screen of the system of FIG. 1;

FIG. 18 is a screen shot depicting an example screw locationdigitization screen during a first step in the Acquire Screws step ofFIG. 15;

FIG. 19 is a screen shot depicting an example screw locationdigitization screen during a second step in the Acquire Screws step ofFIG. 15;

FIG. 20 is a screen shot depicting an example screw digitization screenduring a third step in the Acquire Screws step of FIG. 15;

FIG. 21 is a screen shot depicting an example bend instructions screenin the Bend Instructions step of FIG. 15;

FIG. 22 is a flowchart depicting the steps of the rod bending processaccording to a second embodiment;

FIG. 23 is a screen shot depicting an example Advanced Options menuscreen of the system of FIG. 1;

FIG. 24 is a screen shot illustrating a first example screen of anAdjust Points feature according to one embodiment;

FIG. 25 is a screen shot illustrating a second example screen of theAdjust Points feature of FIG. 24;

FIG. 26 is a screen shot illustrating a third example screen of theAdjust Points feature of FIG. 24;

FIG. 27 is a screen shot illustrating a first example screen of aPre-Bent Preview feature according to one embodiment;

FIG. 28 is a screen shot illustrating a second example screen of thePre-Bent Preview feature of FIG. 27;

FIG. 29 is a screen shot illustrating a third example screen of thePre-Bent Preview feature of FIG. 27;

FIG. 30 is a screen shot illustrating a first example screen of aSagittal Correction feature according to one embodiment;

FIG. 31 is a screen shot illustrating a second example screen of theSagittal Correction feature according to the first embodiment;

FIG. 32 is a screen shot illustrating a first example screen of theSagittal Correction feature according to a second embodiment;

FIG. 33 is a screen shot illustrating an additional example screen ofthe Sagittal Correction feature according to the first and/or secondembodiment;

FIG. 34 is a screen shot illustrating a first example screen of theCoronal Correction feature according to a first embodiment;

FIG. 35 is a screen shot illustrating a second example screen of theCoronal Correction feature according to a first embodiment;

FIG. 36 is a screen shot illustrating a third example screen of theCoronal Correction feature according to the first embodiment;

FIG. 37 is a screen shot illustrating a fourth example screen of theCoronal Correction feature according to the first embodiment;

FIG. 38 is a screen shot illustrating a first example screen of theCoronal Correction feature according to a second embodiment;

FIG. 39 is a screen shot illustrating a second example screen of theCoronal Correction feature according to the second embodiment;

FIG. 40 is a screen shot illustrating a third example screen of theCoronal Correction feature according to the second embodiment;

FIG. 41 is a flowchart illustrating the steps of the Global SpinalBalance feature according to one embodiment;

FIG. 42 is a screen shot illustrating a first example screen of theGlobal Spinal Balance feature in pre-operative mode;

FIG. 43 is a screen shot illustrating a first example screen of theGlobal Spinal Balance feature in target mode;

FIG. 44 is a screen shot illustrating a second example screen of theGlobal Spinal Balance feature in target mode;

FIG. 45 is a screen shot illustrating a first example screen of theGlobal Spinal Balance feature in intraoperative mode;

FIG. 46 is a screen shot illustrating a second example screen of theGlobal Spinal Balance feature in intraoperative mode;

FIG. 47 is a screen shot illustrating a third example screen of theGlobal Spinal Balance feature in intraoperative mode;

FIG. 48 is a screen shot illustrating a fourth example screen of theGlobal Spinal Balance feature in intraoperative mode;

FIG. 49 is a screen shot illustrating a fifth example screen of theGlobal Spinal Balance feature in intraoperative mode;

FIG. 50 is a perspective view of one embodiment of a mechanical rodbender comprising part of the surgical bending system of FIG. 1;

FIG. 51 is a perspective view of a lumbar spine illustrating examplespinal fixation anchors with attached extension guides and an examplerod pusher instrument in use during implantation of a two level fixationconstruct, according to one example;

FIG. 52 is a perspective view of the example rod pusher of FIG. 51;

FIG. 53 is a plan view of an example rod inserter configured for use inthe implantation procedure of FIG. 51;

FIG. 54 is a screen shot illustrating a first example screen of the RodTracking feature according to one embodiment; and

FIG. 55 is a screen shot illustrating a second example screen of the RodTracking feature according to one embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin development of any such actual embodiment, numerousimplantation-specific decisions must be made to achieve the developers'specific goals such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. The systems and methods disclosed herein boast avariety of inventive features and components that warrant patentprotection, both individually and in combination.

With reference now to FIG. 1, there is shown, by way of example, oneembodiment of a surgical bending system 10 including a spatial trackingsystem 12 to obtain the location of one or more surgical implants 14, acontrol unit 16 containing software to convert the implant locations toa series of bend instructions, and a bending device 18 to execute thebend instructions.

Preferably, the spatial tracking system 12 includes an IR sensor 20, adigitizer pointer 23, as well as other components including Host USBconverter 21. The spatial tracking system 12 is in communication withcontrol unit 16. The control unit 16 has spatial relation software andis communicatively linked to the display 32 so that information relevantto the surgical procedure may be conveyed to the user in a meaningfulmanner. By way of example, the relevant information includes, but is notlimited to, spatial positioning data (e.g., translational data in the x,y, and z axes and orientation/rotational data R_(x), R_(y), and R_(z))acquired by the IR sensor 20. According to one or more embodiments, thesystem 10 comprises a neuromonitoring system communicatively linked tothe spatial tracking system 12 via the control unit 16. By way ofexample only, the neuromonitoring system may be the neuromonitoringsystem shown and described in U.S. Pat. No. 8,255,045, entitled“Neurophysiologic Monitoring System” and filed on Apr. 3, 2008, theentire contents of which are hereby incorporated by reference as if setforth fully herein.

FIGS. 2-9 depict the various components of one or more digitizerpointers 23 for use with the present invention. FIGS. 2-4 detail anexample IR-reflective tracking array 22 component of the digitizerpointer 23. Array 22 includes a housing 34, bilateral shutters 36, and aplurality of IR-reflective spheres 38 arranged in a calculated manner atvarious locations on the array 22 such that their position informationis selectively detectable by the IR sensor 20. Housing 34 comprises atop housing 40, bottom housing 42, and a distal threaded aperture 56configured to threadably receive the threaded end 78 of a stylus (e.g.,stylus 24, 26, 28, and/or 30). Top housing portion 40 is furthercomprised of upper portion 44, underside 46, and sides 48. A pluralityof sphere apertures 52 extend between upper portion 44 and underside 46and are sized and dimensioned to receive reflective spheres 38 withinrecessed pockets 54. Each side 48 includes cutout 50 sized anddimensioned to receive tongue 70. Bottom housing 42 is comprised of afirst face 58 and a second face 60. The first face 58 includes nestingplatforms 62 and bullet posts 64. Each shutter 36 includes handleportion 66, cover portion 68, tongue 70, interdigitating gear teeth 72,and channel 74 for receiving bullet posts 64. A spring 76 extendsbetween the two shutters 36 and is held in place via spring posts 71.

In an assembled state, each IR-reflective sphere 38 is nested on aplatform 62. Top housing 40 is placed over bottom housing 42 in a snapfit configuration such that each IR-reflective sphere 38 fits within arecessed pocket 54 within its respective sphere aperture 52. Accordingto one implementation, bilateral shutters 36 are positioned over thehousing 34 with tongues 70 sliding into cutouts 50 such that eachshutter cover 68 obscures exactly one half of the IR-reflective sphere38 (for example, the middle IR-reflective sphere 38) as depicted in FIG.2.

As depicted in FIG. 5, the IR-reflective tracking array 22 mates withone or more surgical objects (for example styluses 24, 26, 28, 30). Eachstylus 24, 26, 28, 30 includes a threaded proximal end 78 for matingwith the threaded distal aperture 56 of the IR-reflective tracking array22, elongate shaft 80, and shaped distal tip 82. Shaped distal tip 82may be any shape that is complimentary to, and fits securely within, theshape of a particular screw head. For example, FIG. 6 shows styluses 24,26, 28, and 30 each with a different shaped distal tip designed to matewith different open screw systems, minimally-invasive screw systems, andclosed tulip, iliac, and offset connector systems. The distal tip 82 ispreferably inserted into each screw while orienting the digitizerpointer coaxial to that screw (or other fixation device).

According to some implementations (for example, the implementationsshown with respect to styluses 24, 26, and 28), the length of theelongate shaft 80 is fixed relative to the array 22 such that alldigitized points are a consistent length from the geometry of theIR-reflective markers 38 and position information may be obtained fromthis relationship. According to other implementations (for example, theimplementation shown with respect to offset pointer 30), the length ofthe elongate shaft 80 is adjustable relative to the array 22 such asthat shown with stylus 30, effectively elongating the distance from thedigitized point and the IR-reflective markers. This longer distancetranslates to digitization of a point above the actual screw head basedon the distance the user adjusted the elongate shaft 80. As will beappreciated in conjunction with the discussion below, the resulting bendinstructions would shape a rod that traverses that point above the screwallowing the user to reduce the screw to the rod.

As shown in FIGS. 6-8, offset pointer 30 includes an elongate tubularmember 84 and an inner piston 86. Elongate tubular member 84 iscomprised of a milled helical slot 104 and a plurality of offset depthslots 106 located around the helix that correspond to a plurality ofoffset distances as will be described below. Inner piston 86 includesshaft 88, T-shaped cap 92, springs 94, and bushing 96. The T-shaped cap92 is positioned over the proximal end of the shaft 88 and is preferablywelded to the proximal end 105 of the elongate tubular member 84.Springs 94 are slideably positioned along the length of the shaft 88between the distal end 93 of the T-shaped cap 92 and bushing 96. Bushing96 is positioned over the distal end of the shaft 88. Pin 100 is travelsthrough, and protrudes laterally from, slots 90, 98 on the inner shaft88 and bushing 96, thereby securing the bushing 96 to the inner shaft88. The pin 100 is sized and dimensioned such that it travels throughthe helical slot 104 and be positioned within each of the offset depthslots 106.

The offset pointer 30 gives the user the ability to execute plannedscrew movement by a specific amount. The user inserts the offset pointer30 into the screw head. Keeping the distal tip 82 engaged to the screwhead, the user then selects an offset amount to be added to the screwand angles the offset pointer 30 in the direction he or she wishes toapply the offset to. To adjust between offset depth slots 106, the shaft88 is pulled away from the array 22 and twisted until the pin 100 fallsinto the desired offset slot 106. As the shaft 88 is pulled, ittelescopes in and out of the elongate tubular member 84 such that thedistance between the shaped distal end 82 and the array 22 is increased.For purposes of illustration, FIG. 8 shows the offset pointer 30 withthe pin 100 in the 16 mm offset slot 106 corresponding to a 16 mm offsetbetween the pointer 30 length and the IR-reflective array 22. Offsetoptions may be provided, by way of example only from 0 mm to 16 mmoffsets in 2 mm increments. The system 10 will then acquire positioninformation at that

The digitizer pointer 23 may be used to acquire positional informationabout some or all screw locations. According to a preferred embodiment,the shaped distal tip 82 is coaxially aligned into the screw head andthe array 22 is triggered to register the screw point. Screw locationsmay be digitized in a superior-inferior or inferior-superior direction.According to some implementations, the first screw location digitizedcorrelates to the rod insertion direction component of the bendinstructions (described below). Squeezing handles 66 activates thespring mechanism and permits the shutters 36 to open equally via theinterdigitating gear teeth 72 (FIG. 4). Opening the shutter covers 68exposes the middle IR-reflective sphere 38 and allows the IRtrackingarray 22 to be “seen” by the IR sensor 20 and the position of thedigitizer pointer 23 to be digitized. In this way, the IR sensor 20 onlyrecognizes the digitizer pointer 23 once the middle sphere 38 is exposedwhich allows for point-by-point tracking and obviates the sensing anddigitization of one or more unnecessary data points which may occur withprior art systems that continually track surgical objects. Further, useof the gear mechanism allows the passive IR-reflective sphere 38 to be“seen” symmetrically by the IR sensor 20, thereby enabling a moreaccurate calculation of position information by the system 10. Accordingto some implementations, the control unit 16 emits an audible sound tonotify the user that the middle sphere 38 is recognized by the IR sensor20 and the screw point is acquired. Once a point has been registered,the shutter handles 66 may be released, thereby closing the bilateralshutters 36. This process is then repeated for all screw locations to bedigitized.

In accordance with the present invention, there are provided a pluralityof algorithms for achieving rod bends. The surgical bending algorithmsmay be divided into two smaller sub-systems: (1) the spatial locationalgorithms that acquire, collect, and digitize points in space and (2)the bending algorithms that analyze the points and calculate the bendinstructions and rod length needed to bend a rod with the mechanicalbending device 18.

As set forth above, the spatial tracking system 12 measures the sixdegrees of freedom (6 DOF) information for the tracked IR-reflectivespheres 38. These data provide the full pose (position and orientation)of each screw of interest which may then be made available to thealgorithm library to calculate the bend instructions. FIG. 10 is a flowchart indicating the steps of the spatial location data acquisitionprocess according to one embodiment. The system 10 initializes thesensor objects from configuration to connect to, control, and read datafrom the IR sensor 20 (step 140). The system 10 then inspects alldevices connected to it and finds the device with a device ID thatcorresponds to the IR sensor 20 (step 141). At step 142, if an IR sensor20 is found at step 141, the system 10 continues to establish aconnection with the IR sensor 20 (step 143). However, if not the system10 continues to search. After the system 10 connects to the IR sensor20, it then loads a tool file that defines the array 22 (step 144).After initialization and tool file loading, the IR sensor 20 mustprepare for taking data. At step 145, the IR sensor 20 is enabled andready to generate positional data but is left idle until tracking isenabled. By way of example and as described with reference to FIG. 17,selecting the position of the IR sensor 20 with respect to the patient'sbody causes the control unit 16 to send the IR sensor 20 a command tobegin tracking. With tracking enabled (step 146), the IR sensor 20 maybe polled to for data (step 147). Preferably, new data is requestedtwenty times per second from the IR sensor 20. At step 148, the datagenerated from polling the IR sensor 20 is checked to ensure that it isreporting valid data. The data may be considered valid if all of theIR-reflective spheres 38 are visible to the IR sensor 20, the digitizerpointer 23 is fully inside the IR sensor's 20 working volume, there isno interference between the IR sensor 20 and the digitizer pointer 23,and both the location and rotation information reported are not null. Atstep 149, if the data is not deemed valid, then the digitized point isnot used by the system 10 and polling is resumed. If the fifthIR-reflective sphere 38 (i.e. the middle sphere) is visible on thedigitizer pointer 23 (step 150), the process of collecting positionaldata for the bend algorithm commences. If the middle sphere 38 is notvisible, then the data is available to the system 10 only to showproximity of the IR sensor 20 and IR-reflective tracking array 22 (step151). Points used by the bend algorithm are preferably an average ofseveral raw elements (step 152). Normally, five points are collected atthis step before the points are processed and made available to the bendalgorithm. The position data is averaged using a mean calculation. Thedirections are averaged in the quaternion representation (raw form) thenconverted to a unit direction vector. The data is rotated from thespatial tracking system 12 coordinate from into the system 10 coordinateframe using a rotation matrix. At step 153, after all processing, thedata is available for the bend algorithm to collect and process furtheras will be described in greater detail below.

The surgical bending software takes the location and direction data ofthe screw locations as described above and uses one or moregeometry-based algorithms to convert these relative screw locations intoa series of bend instructions. FIG. 11 is a flow chart indicating thesteps of the surgical bending process according to a first embodiment.At the input validation step 154, the system 10 may validate the systeminputs to ensure the rod overhang is greater than zero, validate thesensor setup to ensure that the IR sensor 20 location has been set, andvalidate each of the acquired points. By way of the example, thevalidation of each of the acquired points ensures, for example, thatthere are at least two screw points digitized, no two screw locationsare too far apart, no two screw locations are too close together, andthe span between the superior-most and inferior-most screw locations isnot longer than the longest available rod.

At the transformation step 155, the data may be centered and alignedsuch that the first data point acquired is set at the system 10coordinate's origin and all data is aligned to the x-axis of thesystem's coordinates thereby reducing any potential misalignment of theIR sensor 20 relative to the patient's spine.

At the rod calculations step 156, the system 10 may perform rodcalculations for a straight rod solution, a pre-bent rod solution, and acustom-bend solution. For a straight rod solution, the system 10 firstdetermines the length of a straight rod that will span all of the screwlocations. This length may be calculated to accommodate each of thescrew heads, hex and nose lengths of the rods chosen, and the user'sselected rod overhang length. The system 10 then fits the data to astraight line, if the screw data is within tolerance of the straightline, then the bend instructions will return a straight rod, otherwiseit will return no rod solution and proceed to look for a pre-bent rodsolution. By way of example only, the tolerance may be 2 mm in each ofthe sagittal and coronal planes.

For a pre-bent rod solution, the system 10 first determines the lengthof the shortest pre-bent rod from the available rod from the availablerods (as will be described in greater detail below) that will span allof the screw locations. This length may be calculated to accommodateeach of the screw heads, hex and nose lengths of the rods chosen, andthe user's selected rod overhang length. Next, the system 10 fits thedigitized screw data to a circular arc in 3-dimensional space. If thescrew data is within the tolerance of the arc, then the bendinstructions will return a pre-bent rod solution, otherwise it willreturn no rod solution and proceed to look for a custom-bend rodsolution. By way of example, this tolerance may be 2 mm in each of thesagittal and coronal planes.

FIG. 12 depicts a flow chart of a custom bend algorithm according to oneembodiment. At step 158, screw location and direction data is generatedby the spatial tracking system 12 as set forth above. The data is thenprojected into two planes: the x-y plane (coronal view) and the x-zplane (sagittal view). Each projection is then handled as a 2D data set.At step 159, a fixed size loop is generated over small incrementaloffsets for the first bend location for the end of the rod whichoptimizes the ability of the bend reduction step 162 to make smoothsolutions. At step 160, the system 10 creates a spline node at eachscrew location and makes a piecewise continuous 4^(th) order polynomialcurve (cubic spline) through the screw points. At step 161, the smooth,continuous spline is sampled at a regular interval (e.g., every 1 cm)along the curve to generate an initial set of proposed bend locations.At step 162, as many bends as possible are removed from the initial setof proposed bend locations from step 161 as possible to reduce thenumber of bends the user must execute on a rod in order to fit it into ascrew at each digitized screw point. According to one embodiment, nobend is removed if eliminating it would: (1) cause the path of the bentrod to deviate more than a predefined tolerance limit; (2) cause any ofthe bend angles to exceed the maximum desired bend angle; and (3) causethe rod-to-screw intersection angle to exceed the maximum angulation ofthe screw head. Once the number of bends has been reduced, the 2D datasets are combined and handled as a 3D data set. The 3D line segments arethen evaluated based on distance between each line segment interaction(Location), the angle between two line segments (Bend Angle), and therotation (Rotation) needed to orient the bend into the next bend planeusing the following calculations:Location: ((X ₂ −X ₁)²+(Y ₂ −Y ₁)²+(Z ₂ −Z ₁)²)^(1/2)Bend Angle: arc-cosine(V ₁₂ ·V ₂₃)

-   -   where · is the dot product and V is a vector between 2 points        Rotation: arc-cosine(N ₁₂₃ ·N ₂₃₄)    -   where · is the dot product and N is the normal vector to a plane        containing 3 points.        These calculated numbers are then tabulated to the physical        design of the rod bender 18 and the selected rod material and        diameter. Bend angles account for the mechanical rod bender's 18        tolerance and will account for the rod's material and diameter        based on previous calibration testing performed with mechanical        rod bender 18 and the specific kind of rod. Calibration testing        quantifies the amount of spring-back that is expected when        bending a certain rod material and diameter. By way of        illustration, a 5.5 mm diameter titanium rod's spring-back can        be characterized by a 1^(st) order linear equation:        BA _(A)=0.94*BA _(T)−5.66        where BA_(T) is the theoretical bend angle needed that was        calculated from the 3D line segment and BA_(A) is the actual        bend angle needed to bend the rod to so it can spring back to        the theoretical bend angle. Thus, using this equation, when 20        degrees of bend is calculated from the 3D line segment above,        the “spring-back” equation for that rod will formulate that a 25        degree bend needs to be executed in order for it to spring-back        to 20 degrees. The length of the final rod is the total of all        the calculated distances plus the selected rod overhang.

Once all of the rod solutions have been generated, the loop is completed(step 163). At step 164, from all of the rod solutions generated in theloop above, the system 10 may output the rod solution having thesmallest maximum bend angle (i.e., the smoothest bent rod). It is to beappreciated that the system 10 may choose the rod solution displayedbased on any number of other criteria. At step 169, the system 10 thengenerates the three-dimensional locations of the bends in space.

Referring back to the flow chart of FIG. 11, from the geometric bendlocations and/or pre-bent rod output of the rod calculations step 156above, the system 10 generates instructions for the user to choose astraight rod, a pre-bent rod, or to custom bend a rod (step 157). All ofthe output instructions are human-readable strings or characters. In allcases, the length of the required rod is calculated as described aboveand is displayed to the user as either a cut rod or standard rod. Forcustom bend solutions, rods are loaded into the bender with the“inserter end” (e.g., one pre-determined end of the rod) into the bendercollet 126. If, due to geometric constraints, the rod cannot be bentfrom the inserter end, then the instructions are flipped, and the cut(or nose) end of the rod is instructed to be put into the bender collet126. The bend instructions are generated from the geometric bendlocations and are given as “Location”, “Rotation”, and “Bend” values aswill be described in greater detail below. These values correspond tomarks on the mechanical bender 18.

FIGS. 13-14 depict a flow chart of a second embodiment of a custom bendalgorithm. In accordance with this second embodiment, the custom bendalgorithm includes a virtual bender used to render a virtual rod. Thefollowing calculations and the flowcharts of FIGS. 13-14 highlight thesteps of this embodiment.

The 3D vector s_(i)=[s_(i) ^(x), s_(i) ^(y), s_(i) ^(z)]^(T) denotes thei'^(th) screw digitized by the user such that the set of N acquiredscrews that defines a rod construct may be denoted ass=[s ₀ , . . . ,s _(N−1)]ε

^(3×N)  (1)It may be assumed that the screws have been collected in order (e.g.superior-most screw to inferior-most screw or inferior-most screw tosuperior-most screw) so the index i can also be thought of as the indexthrough time.

A virtual rod (R) of length L_(r) given in mm is broken down into Nruniformly distributed points, R=[r₀, . . . , r_(Nr-1)]. Each rod pointr_(i) is composed of two components, a spatial component and adirectional component r_(i)={r_(i) ^(s),r_(i) ^(d)}, where r_(i) ^(s),r_(i) ^(d)ε

³. The segments between rod points is constant and defined byδ_(i) =|r _(i+1) ^(s) −r _(i) ^(s)|. Let Δ_(d)=Σ_(i=0) ^(d)δ_(i), thenΔ_(N) _(r) ⁻¹ =L _(r).

A virtual bender (B) consists of a mandrel (M) of radius M_(r) (mm).Preferably, though not necessary, the key assumption when bending thevirtual rod around M is the conservation of arc length. For illustrativepurposes only, if a 90° bend is introduced to an example rod R of length100 mm around a mandrel with radius 10 mm to produce a rod {circumflexover (R)}, then∫dR=∫d{circumflex over (R)}.  (2)

The virtual rod, R, is bent according to a list of instructions. Eachinstruction consists of a location (I_(l)), rotation (I_(r)), and bendangle (I_(θ)). The location is the position of the rod in the bender andcorresponds to the point directly under the mandrel M. The rotation isgiven in degrees (0°-360°) and corresponds to the amount the rod isrotated from 0 in the collet. The bend angle is given by a single letterthat corresponds to a specific angle in degrees. There is acorresponding notch on the bender with the same letter for the user toselect.

The rod is initialized (step 166) such that the spatial component r_(i)^(s)=[Δ_(i),0,0]^(T)┘_(i=0) ^(N) ^(r) ⁻¹, and the direction componentr_(i) ^(d)=[0,1,0]^(T)|_(i=0) ^(N) ^(r) ⁻¹ which effectively orients thevirtual rod to be at zero rotation in the virtual bender. For each bendinstruction (step 167), the system 10 rotates the virtual rod around thex-axis by I_(r) (step 168). The system 10 finds the point {circumflexover (r)}_(i) that matches I_(l). The virtual rod is translated by−{circumflex over (r)}_(i). Next, each rod point from i to i+M_(r)*I_(θ)is projected onto the mandrel M while preserving segment length (step169-170). The virtual rod is then rotated around the x-axis by angle−I_(r). Next, the system 10 checks that r₀ ^(d)=[0,1,0]^(T) to verifythat the virtual rod in the collet has the correct direction vector(step 171). At this point, R has approximated the geometry of the rod asit would be bent in the physical mechanical bender 18.

The next step is to align the bent virtual rod to the acquired screwpositions (step 172). According to one embodiment, the alignment processhas two stages—first, the system 100 finds the optimum rotation coarsescale (step 174). Second, the system performs the iterative closestpoint iteration algorithm fine scale.

Preferably, the system first initializes the result close to a globalminimum (step 173). In the rod alignment algorithm, this initializationfollows the approach described below:

Using the arc length of the custom rod and the arc length of the screws,putative matches from the screws to the rod are produced. This producestwo 3D point sets of equal size. Given two 3D mean centered point setsΣ=[σ₀, . . . , σ_(N−1)] and Γ=[γ₀, . . . , γ_(N−1)], then in the leastsquares sense, it is desirable to minimize

$\begin{matrix}{E = {\frac{1}{N}{\sum\limits_{i = 0}^{N - 1}\;{\left( {\sigma_{i} - {T\;\gamma_{i}}} \right)^{T}\left( {\sigma_{i} - {T\;\gamma_{i}}} \right)}}}} & (3)\end{matrix}$Where T denotes the rotation matrix. Let {circumflex over (T)} denotethe optimum 3D rotation matrix, then

$\begin{matrix}{T = {\arg\limits_{T}\;\min\frac{1}{N}{\sum\limits_{i = 0}^{N - 1}\;{\left( {\sigma_{i} - {T\;\gamma_{i}}} \right)^{T}\left( {\sigma_{i} - {T\;\gamma_{i}}} \right)}}}} & (4)\end{matrix}$It turns out that {circumflex over (T)}=UV^(T), whereC=SVD(H)=UΣV ^(T)  (5)and

$\begin{matrix}{H = {\frac{1}{N}{\sum\limits_{i = 0}^{N - 1}\;{\sigma_{i}^{T}{{\gamma_{i}\left( {{step}\mspace{14mu} 174} \right)}.}}}}} & (6)\end{matrix}$

Due to error potentially introduced by differences in arc length, theproposed solution may not be the global minimum. Thus, the following arerepeated until convergence (step 175):

For each s_(i), find the closest r_(j) (step 176)

Calculate the residual vector e_(i)=s_(i)−r_(j)

Calculate the average residual vector

$\hat{e} = {\frac{1}{N}{\sum\limits_{i = 0}^{N - 1}\;{e_{i}\left( {{step}\mspace{14mu} 177} \right)}}}$

Translate the rod by ê (step 178)

Verify the error is reduced (step 179).

Next the virtual rod is rendered at step 180. The curve may besimplified for rendering purposes by traversing each triad of rod pointsand calculating the angle between the two vectors. If the first triad is{r₀, r_(i), r2}, the two vectors are formed as v=r₁−r₀ and w=r₂−r₀. If|v×w|=0, then the middle point of the triad (in this case r₁) isredundant, provides no new information to the geometry of the rod andmay be removed.

It will be appreciated that, in accordance with this embodiment of therod bending algorithm, the virtual bender may be capable of bending arod at any location of any angle perfectly to observe arc length. Usinga virtually bent 3D rod to determine problem screws (i.e. screwlocations with a high screw-rod fit error) may give an accurate fitbetween the actual screws and actual rod before the actual rod is bent.This may be particularly advantageous in certain surgical applicationswhere it is desirable to quantify the amount of offset between a rodsolution and the digitized screw locations as well as input one or moresurgical parameters into the rod bending calculation.

In accordance with the present invention, there is described a thirdembodiment of an algorithm for generating a custom bend which may beutilized in conjunction with the second embodiment. The approach isdirected to one or more algorithms that sample from probabilitydistributions and employ random sampling to obtain a numerical result. AMarkov chain is a sequence of random variables, X₀, X₁ . . . , such thatthe current state, the future and past states are independent.p(X _(n+1) =x|X ₀ =x ₀ ,X ₁ =x ₁ , . . . ,X _(n) =x _(n))=p(X _(n+1)=x|X _(n) =x _(n))  (1)

Given an ordered set of screws that define a constructS=[s ₀ . . . ,s _(N−1)]ε

^(3×N)  (2)where s_(i)=[s_(i) ^(x), s_(i) ^(y), s_(i) ^(z)]^(T) denotes the i^(th)3D screw digitized by the user, the system 10 finds the set of bendinstructions that define a rod that fits the screws in an optimum waydefined by an error function. It is to be appreciated that the search ofthe bender space is quite complex as there are several constraints thatmust be observed for the algorithm to produce valid bend instructions(e.g., the bend locations cannot be in close proximity to the screws,the bend locations must be in multiples of 5 mm apart, the bend anglesmust be in multiples of 5°, no bend angle can be greater than 60°,etc.).

In accordance with the second embodiment, the likelihood or errorfunction may be constructed based on how well the virtual rod fits thedata. Here, the rod is fit to the data in the least squares sense. Inthis way, a likelihood function is defined that incorporates, forexample, a prior to prefer fewer bend instructions:

$\begin{matrix}{L = {\prod\limits_{i = 0}^{N_{s} - 1}\;{\frac{1}{\sigma_{s}\sqrt{\pi}}{\mathbb{e}}^{\frac{- {({s_{i} - r_{i}})}^{2}}{\sigma_{s}^{2}}}{\mathbb{e}}^{\frac{- N_{b}}{\alpha}}}}} \\{= {\left( \frac{1}{\sigma_{s}\sqrt{\pi}} \right)^{N_{s}}{\mathbb{e}}^{\sum\limits_{i = 0}^{N_{s} - 1}\;\frac{- {({s_{i} - r_{i}})}^{2}}{\sigma_{s}^{2}}}{\mathbb{e}}^{\frac{- N_{b}}{\alpha}}}}\end{matrix}$such that the log-likelihood function may be defined as

$\begin{matrix}{{\log(L)} = {{{- N_{s}}{\log\left( \sigma_{s} \right)}} - {\sum\limits_{i = 0}^{N_{s} - 1}\;\frac{- \left( {s_{i} - r_{i}} \right)^{2}}{\sigma_{s}^{2}}} - \frac{- N_{b}}{\alpha}}} & (3)\end{matrix}$Where N_(b) denotes the number of bends in the rod, N_(s) denotes thenumber of screw locations, s_(i) is the i'th screw, r_(i) is the i'throd point, and α is the control hyper-parameter for the number of bends(e.g. α=0.05).

As can be seen from equation (3), there has been introduced a prior tocontrol the number of bends introduced into the rod. This probabilisticapproach to bend instruction generation allows for tailoring ofconstraints, for instance, a prior on the severity of the bends couldalso be introduced. Further, a prior could be introduced on how todefine how close to the screws the bends may be located. This prior mayhave a “preferred” value, but probabilistically, there may be an optimalsolution away from this idealized value. By way of example, somehypothesized rules that may be applied to this algorithm include, butare not limited to: birth move: add a bend to the current solution;death move; remove a bend from the current solution; update move:translate rod points along the rod. Use of this embodiment may providemore potential rod solutions to the user.

Details of the surgical bending system 10 are discussed in conjunctionwith a first embodiment of a method for obtaining a custom-fit rod. Thesystem 10 is typically utilized at the end of a posterior or lateralfixation surgical procedure after screws, hooks or other instrumentationhave been placed, but prior to rod insertion. As shown in the flowchartof FIG. 15, the surgical bending system 10 obtains position informationof the implanted screw positions and outputs bend instructions for a rodshaped to custom-fit within those implanted screws. At step 190,pertinent information is inputted into the system via a setup screen. Atstep 192, the user designates which side (left or right) rod will becreated. At step 194, the system 10 digitizes the screw locations. Atstep 196, the system 10 outputs bend instructions. At step 198, the userbends the rod according to the bend instructions. Steps 190-198 may thenbe repeated for the other rod.

FIG. 16 illustrates, by way of example only, one embodiment of a screendisplay 200 of the control unit 16 capable of receiving input from auser in addition to communicating feedback information to the user. Inthis example (though it is not a necessity), a graphical user interface(GUI) is utilized to enter data directly from the screen display 200. Asdepicted in FIG. 16, the screen display 200 may contain a header bar202, a navigation column 204, device column 206, and a message bar 208.

Header bar 302 may allow the user to view the date and time, altersettings, adjust the system volume, and obtain help information via dateand time display 210, settings menu 212, volume menu 214, and help menu216 respectively. Selecting the settings drop-down menu 212 allows theuser to navigate to system, history, and shutdown buttons (not shown).For example, choosing the system button displays the rod bendingsoftware version and rod bender configuration file; choosing theshutdown option shuts down the rod bending software application as wellas any other software application residing on the control unit 16 (e.g.a neuromonitoring software application); and choosing the history optionallows the user to navigate to historical bend points/instruction datain previous system sessions as will be described in greater detailbelow. Selecting the help menu 216 navigates the user to the system usermanual. As will be described in greater detail below, navigation column204 contains various buttons (e.g., buttons 218, 220, 222, 224, 226) fornavigation through various steps in the rod bending process. Pressingbutton 204 expands/minimizes the details of the navigation column.Devices column 206 contains various buttons indicating the status of oneor more devices associated with the surgical bending system 10. By wayof example, devices column 206 may include buttons 228 and 230 for thedigitizer 23 and IR sensor 20 components of the system 10, respectively.Pressing button 206 expands/minimizes the details of the devices column.Furthermore, pop-up message bar 208 communicates instructions, alerts,and system errors to the user.

FIGS. 16-17 depict an example setup screen. Upon selecting setup button218 on the display screen 200, the surgical bending system 10automatically initiates the setup procedure. The system 10 is configuredto detect the connection status of each of its required components. Byway of example only, icons 228, 230 indicate the connectivity andactivity status of the digitizer 23 and IR sensor 20, respectively. Ifone or more required components are not connected or are connectedimproperly, the display 200 may alert the user to address the issuebefore proceeding via textual, audio, and/or visual means (e.g., textualmessages, audible tones, colored icons or screens, blinking icons orscreens, etc.). According to one embodiment, the digitizer icon 228 is astatus indicator for the active acquisition and/or recognition of thedigitizer and the presence and background color of the icon 228 maychange to indicate the digitizer tracking status. By way of example, theicon 228 may be absent when the system 10 is not acquiring screws anddoes not recognize the digitizer, gray when the system 10 is notacquiring screws and recognizes the digitizer, green when the system 10is in screw acquisition mode and recognizes the digitizer, and red whenthe system 10 is in screw acquisition mode and does not recognize thedigitizer. Pressing button 206 expands minimizes the details of thedevice column 206. Depending on the type of surgery, type of patientdeformity, etc., it may be advantageous for the user to choose adigitizer from a selection of different digitizers. According to oneembodiment, pressing icon 228 expands a pull-out window for thedifferent stylus options available with the rod bending system 10 (e.g.,styluses 22, 24, 26, 30 as described above). According to anotherembodiment, the IR sensor graphic icon 230 is a status indicator for theIR sensor 20. The presence and background color of the icon 230 maychange to indicate the status of the IR sensor 20. By way of example,the icon 230 may be absent when the system 10 does not recognize the IRsensor 20, gray when the system 10 recognizes the IR sensor 20 isconnected to the system 10, and red when the system 10 senses acommunication or bump error for the IR sensor 20. Preferably, the IRsensor 20 should be recognized if it is connected after initializationof the bending application.

With all of the required components properly connected to the surgicalbending system 10, the user may then input one or more pieces ofcase-specific information from one or more drop-down menus. By way ofexample, drop-down menus for rod system 234, rod material/diameter 236,rod overhang 238, procedure type (not shown), and surgical levels) maybe accessed from the setup selection panel 232 of the screen display200. The rod system drop-down menu 234 allows the user to choose the rodsystem he/she plans to use. This selection drives choices for the rodmaterial/diameter 236 drop-down menus. By way of example, under the rodsystem drop-down menu 234, the system 10 may be programmed with numerousfixation options from one or more manufacturers. Alternatively, it maybe programmed with the fixation system selections for one manufactureronly (e.g. NuVasive® Precept®, Armada®, and SpherX® EXT). The user mayalso choose the combination of rod material (e.g. titanium, cobaltchrome, etc.) and rod diameter (e.g. 5.5 mm diameter, 3.5 mm diameter,etc.). The drop-down menu 238 for material and diameter options maypreferably be dependent upon the choice of rod system. Because thegeometry and sizes can vary between manufacturers and/or rod systems,programming the system 10 with these specific inputs can aid inoutputting even more accurate bend instructions. The user may alsochoose the amount of overhang from the rod overhang pull-down menu 238.By way of example, the amount of overhang may be selectable in 0 mm, 2.5mm, 5 mm, 7.5 mm, and 10 mm lengths. According to one embodiment, thisfunction prescribes a symmetric overhang on both the superior andinferior ends of the rod. According to another embodiment, this functionalso prescribes different overhang lengths on either end of the rodbased on user preference and patient anatomical considerations. Althoughnot shown, the system 10 also contains functionality for accommodatingmultiple rod diameters and transitional rods as used, for example inOccipital-Cervical-Thoracic (OCT) fusion procedures.

After the setup inputs have been inputted into the setup selection panel232, the surgical bending system 10 aids the user in setting up the IRsensor 20 in an optimal position for positional data acquisition. It isto be appreciated that any visual (textual, graphic) indicator may beused to indicate the IR sensor placement instructions. According to someimplementations, an active graphic directs the user to position the IRsensor 20 relative to the digitizer array 22 held static within thepatient's body. As shown in FIG. 17, the user first selects the side ofthe patient the IR sensor 20 is located on by selecting the left sidesensor position button 242 or right side sensor position button 244 inthe IR sensor setup panel 240. Choosing the left or right side sensorposition button 242, 244 activates a the IR sensor positioning panel 246such that IR sensor graphic 248 and a tracking volume box graphic 250appear on the display screen 200. Tracking volume box 252 that moveswith the IR sensor graphic 248 as the IR sensor 20 is moved. Next, theuser positions the digitizer array 22 into the body of the patient. Oncerecognized by the system 10, a target volume box 252 (which may bedisplayed as white in color) is positioned over the patient graphic 254.Next, the user moves the IR sensor 20 relative to the digitizer array 22until the tracking volume box 250 matches up to the position of thetarget volume box 252. According to some implementations, the IR sensorgraphic 248 increases in size if it is moved superior to the targettracking volume and decreases in size if it is moved inferior to thetarget volume. According to some other implementations, the trackingvolume box 250 may be color-coded to depict the relative distance to thetarget volume. By way of example, the tracking volume box 250 may bedepicted in red if the distance to the target volume is outside of acertain distance in one or more axes (e.g., outside ±8 cm in all 3axes.) and green if within or equal to ±8 cm in all 3 axes. Once theoptimal position of the IR sensor 20 has been ascertained, the setupprocess is complete.

Once the user has completed all of the required steps in the setupscreen, a graphic (e.g., a check) may appear on setup button 218 toindicate such a completion and the system 10 proceeds to step 192 in theflowchart of FIG. 15. Using the GUI, the user designates which side ofthe patient's spine to acquire digitized positional information from byselecting either the Left “L” toggle/status button 220 or Right “R”toggle/status button 222. The user then selects the Acquire Screwsbutton 224 which navigates the display screen 200 to an Acquire Screws(left or right) screen shown by way of example in FIGS. 18-20. InAcquire Screws mode, the display screen 200 includes a sagittal viewpanel 256 and a coronal view panel 258 with spine graphics 260, 262 ineach of the sagittal and coronal views, respectively. Spine graphic 260may flip orientation depending on which side of the spine the user isdigitizing (left or right). Additionally, spine graphic 262 mayhighlight the side of the patient the user is digitizing (left orright). The user may digitize the location of each implanted screwusing, by way of example, the digitizer pointer 23 as described above.As each screw point 264 is digitized, its relative location with respectto the other acquired screw points 264 can be viewed in both sagittaland coronal views via the sagittal view panel 256 and the coronal viewpanel 258 as shown in FIG. 19. Optionally, the last screw pointdigitized may have a different graphic 266 than the previously-acquiredscrew points 264 (by way of example, the last screw point acquired 266may be a halo and the previously-acquired screw points 264 may becircles). The screws locations may be digitized from asuperior-to-inferior or inferior-to-superior direction and according tosome embodiments, the system 10 can detect which direction thedigitization is occurring in after the acquisition of two consecutivescrew point locations. If during the digitization process, the userwishes to delete a digitized screw point, he/she may do so by pressingthe “Clear Point” button 270. If the user wishes to delete all digitizedscrew points, he/she may do so by pressing the “Clear All Points” button268.

Once the digitized screw points 264 are deemed acceptable, the user maypress the “Calculate Rod” button 272 which initiates the curvecalculation preferably using one of the algorithms discussed above. Oncea rod solution has been calculated, a rod graphic 274 populates throughthe screw points 264, 266 and a confirmation graphic (e.g., a check) mayappear on the “Acquire Screws” button 224 to indicate that the system 10has generated a rod solution. Simultaneously, the “Calculate Rod” button272 becomes the “Undo Rod” button 272. If the user presses the “UndoRod” button 272, the rod solution 274 is cleared and the user mayacquire more screw points or clear one or more screw points. After the“Undo Rod” button 272 is pressed, it then changes back to the “CalculateRod” button 272. Optionally, the system 10 may include a visual graphicfor where along a rod the curve calculation is generating a severe bend(acute angle). The user may select “Undo Rod” button 272, perform one ormore surgical maneuvers (e.g. reduce the screw, backup the screw, adjustthe screw head, etc.), redigitize the screw point, and generate a morefeasible solution. If the rod solution is acceptable to the user, theScrew Acquisition step 194 is complete and the system 10 proceeds theBend Instructions step 196 in the flowchart of FIG. 15.

The user then selects the “Bend Instructions” button 226 which navigatesthe display screen 200 to a Bend Instructions (left or right) screenshown by way of example in FIG. 21. The bend instructions within thebend instructions panel 276 allows the user to view the bendinstructions corresponding to the resulting rod solution in the AcquireScrews screen (FIG. 20). By way of example, the bend instructions panel276 contains three fields containing various aspects of the bendinginstruction: upper message field 278, bender instructions field 280, andlower message field 282. By way of example, the upper message field 278may communicate the rod cut length, rod type, and/or rod loadinginstructions to the user (e.g. “Cut Rod: 175.00 mm Load Inserter EndInto Bender”). The bender instructions field 280 displays rows 284 ofbend maneuvers in location 286, rotation 288, and bend angle 290 toperform on the mechanical bender 18 as will be described in greaterdetail below. In the example shown in FIG. 21, there are five rowsindicating five bend instructions. The lower message field 282 maycommunicate the direction of insertion or orientation of implanting therod to the user. For example, the lower message field 282 shown in FIG.21 provides the following sample instruction: “Insert Rod head to foot.”In some implementations, the rod insertion direction into the patient isdependent on the sequence of screw digitization (superior-to-inferior orinferior-to superior). According to one or more preferred embodiments,the bend instruction algorithm takes into account the orientation of theinferior, superior, anterior, and posterior aspects of the rod andensures that these aspects are known to the user. As the instructionsfor use direct the user to load the rod into the bender, the system 10manages which bends are imparted on the rod first based on the severityof the bend angles. The section of the bend instructions with greaterbend angles may be performed first then the straighter bend sections ofthe bend instructions are performed last. Further, the instructions mayalso direct the user to align a laser line or orientation line on therod to an alignment arrow (not shown) on the mechanical rod bender 18.This alignment controls the Anterior/Posterior orientation of the rodgeometry and generates bend instructions accordingly. The user followsthe bend instructions generated by the system 10 for location (locationmay be color-coded on the bender 18 and on the screen 200 as greentriangle), rotation (rotation may be color-coded on the bender 18 and onthe screen 200 as red circle), and bend angle (bend angle may becolor-coded on the bender 18 and on the screen 200 as blue square),sequentially, starting at the first bend instruction and workingsequentially until the final bend is completed. From here, the user mayrepeat steps 190-198 on the construct for the opposite side of thespine.

Within a surgical procedure, a user may wish to toggle between left andright screens to view left and right digitized screw points, rodpreviews, and bend instructions for reference or comparison. Selectingthe Left “L” toggle/status button 220 and right “R” toggle/status button222 allows the user to do so. According to one more implementations, theGUI may additionally include a History feature. Selecting the Historybutton (not shown) will allow the user to refer back to any previous rodbending solution. The user navigates to the Bend Instructions screen 226based on choice of the L/R toggle buttons 220,222 and pressing BendInstruction button 226. If navigating to previous bend instructions, theBend Instructions screen will display previous bend instructions. Oncethe user has selected the desired rod solution, the user then executesthe bends using the mechanical bender 18.

The embodiments described with respect to FIGS. 15 and 18-21 abovecontemplate digitizing the implanted screw positions and outputting bendinstructions for a rod shaped to custom-fit within those implantedscrews. In one or more additional embodiments, the system 10 obtainsposition information of the implanted screws (steps 192 and 194),accepts correction inputs via one or more advanced options features(step 195), and generates for viewing bend instructions for a rod shapedto fit at locations apart from those implanted screw positions (step196) as depicted in the flowchart of FIG. 22. Installing a rod shaped inthis manner could correct a curvature or deformity in the patient'sspine according to a user's prescribed surgical plan. Details of thesurgical bending system 10 are discussed now discussed with examples forobtaining a rod bent according to one or more surgical plans.

As depicted in FIG. 23, selecting the “Advanced Options” button 292expands an Advanced Options menu 294 from which the user may perform oneor more corrections to the digitized screw points and the system 10generates bend instructions that will achieve those desired correctionson the patient's spine once the rod is implanted and the screws arebrought to the rod.

In some surgical procedures, a user may wish that the rod bend solutionwill consider a point that is not a digitized screw point in determiningthe bend instructions. According to some implementations, this point isan adjusted distance from the digitized screw point location. Selectingthe “Adjust Points” button 296 from the Advanced Options menu 294navigates the user to an Adjust Points screen as depicted in FIG. 23.Selecting a digitized screw location of interest (for example the screwpoint represented as dot 304 in FIG. 24) highlights the screw point andbrings up an adjust points control 306 in each of the sagittal andcoronal views 256, 258. The user adjusts point 304 to its desiredlocation in the sagittal and coronal planes using arrows 308, 310, 312,and 314. In some implementations, as the point moves, dot 304 changescolor based on the distance from the originally digitized screw locationas shown in FIG. 25. Preferably, that color corresponds to color-codedoffset distance indicator 322 which provides visual feedback to the useras to the distance the point has been adjusted. As depicted by way ofexample, dot 304 appears yellow in FIG. 25 indicating that the point hasmoved 4 mm in each of the sagittal and coronal planes. In someimplementations, the system 10 may have a maximum distance from thedigitized point past which it will not allow the manipulated point toexceed (by way of example only, this distance may be 5 mm). The user mayadjust as many points as desired in this fashion. The user may reset alladjusted points to their original configurations via “Reset” button 316or may undo the last adjusted point via the “Undo Last” button 318. Oncesatisfied with the adjusted points, the user may either proceed to oneor more additional advanced options as set forth below or select“Calculate Rod” 272. Once “Calculate Rod” 272 has been selected, thesystem 10 generates a rod in which the curve traverses the adjustedpoints, as in FIG. 26, thereby creating a correction-specific rod andproviding the user with the ability to correct the curvature ordeformity in the spine to his or her prescribed curve.

According to other implementations, a user may wish for a smoother rodbend. When the “Virtual Point” button 320 (shown by way of example inFIG. 25) is selected, the system 10 allows the user to add an additionalpoint anywhere in between the superior-most and inferior-most digitizedscrew locations. While there is no screw at this location, this point istaken into consideration during the curve calculation and may coerce thecurve into a more natural shape yielding a smoother rod bend. Oncesatisfied with the virtual points, the user may either proceed to one ormore additional advanced options as set forth below or select “CalculateRod” 272 and as described above, the system 10 generates acorrection-specific rod solution 274 that the user may use to correctthe spine to the shape of the rod.

It may be advantageous for some patient anatomies for a user to use apre-bent rod. Use of a pre-bent rod eliminates the need for makingadditional bends to a rod while assuring that a desirable rod curve isachieved. After all screw points have been digitized in the AcquireScrews step 194, selecting the “View Pre-Bent Rod” button 298 from theAdvanced Options menu 294 navigates the user to a “View Pre-Bent Rod”screen as depicted in FIGS. 27-28. Based on the digitized screwlocations shown in FIG. 27, the system 10 calculates and outputs thebest pre-bent rod geometry based on the selected manufacturer's rodsystem that was chosen during the setup step 190 (e.g. NuVasive®Precept®) and displays the best fit virtual pre-bent rod solution 324available on top of the digitized screw points for viewing in thesagittal and coronal views 256, 258 (see FIG. 28). Preferably, thesystem 10 only generates a pre-bent rod solution if the geometry of thepre-bent rod fits the digitized screw points within a predeterminedcurve fitting tolerance (e.g. 7 mm). According to one or moreembodiments (as depicted in FIG. 28), a color-coded offset distanceindicator 322 may provide the user with an indication of the distanceeach screw position will be from the pre-bent rod construct. If the useris satisfied with the pre-bent rod suggestion, the system 10 proceeds tothe Bend Instructions step 196 which displays the corresponding pre-bentrod specifications in the Bend Instructions Screen (FIG. 29). The uppermessage field 278 instructs the user that, based on the digitized screwpoints, an 85.0 mm pre-bent rod is recommended. From here, the user maydecide whether the patient's anatomical and surgical requirements wouldbe better suited with a pre-bent option or a custom-bent option. Armedwith the information from FIGS. 27-29, the user may then adjust thescrew positions to fit the pre-bent rod if needed (e.g., adjust thescrew head, adjust the screw depth, etc.).

In some instances, a user may want to align or correct the patient'sspine in the sagittal plane (i.e., add or subtract lordosis orkyphosis). The surgical bending system 10 includes a sagittal correctionfeature in which the user is able to measure the amount of lordosis inthe spine and adjust angles in the sagittal plane. The system 10 thenincorporates these inputs into the bend algorithm such that the rodsolution includes the desired alignment or correction.

Selecting the “View Vectors” button 300 from the Advanced Options menu294 initiates the sagittal correction feature. The user may select atleast two points of interest and the system then determines theappropriate vector in the sagittal view. According to the embodimentshown in FIGS. 30-31 and 33, the angles are measured and adjusted basedon the screw trajectory screw axis position) using the digitized screwdata acquired in the Acquire Screws step 194. As shown in FIG. 30, theuser selects at least two screw points of interest (e.g., screw points338 and 342). The system 10 then measures the angle between the screwtrajectories (shown here as 35 degrees). In some implementations, thesystem 10 may measure the total amount of lumbar lordosis by measuringthe lumbar lordosis angle 334 in the superior lumbar spine (shown inFIG. 30 as 15 degrees) and the lumbar lordosis angle 336 in the inferiorlumbar spine (show in FIG. 30 as 35 degrees). Using the angle adjustmentbuttons 328, 330 on the Angle Adjustment Menu 326, the user may increaseor decrease the desired angle correction of the spine in the sagittalplane (i.e., add or subtract lordosis or kyphosis superiorly orinferiorly). As the angle is adjusted, the angular position 336 betweenthe two screw points 338, 342 is changed as well. FIG. 31 illustrates anexample in which the angular position 336 between points 338 and 342 isincreased to 50 degrees). The system 10 may include a color-coded offsetdistance indicator 322 to provide the user with an indication of thedistance each digitized screw position will be adjusted in the sagittalplane as described above. Once the desired amount of angular correctionis achieved, the user may select the “Set” button 332, and then the“Calculate Rod” button 270. The system 10 then displays a rod solution274 incorporating the user's clinical objective for correction of thespine in the sagittal plane as depicted in FIG. 33.

According to the embodiment of the sagittal correction feature shown inFIG. 32, the superior and inferior lumbar lordosis angles 334, 336 aremeasured, displayed, and adjusted referencing anatomy from an importedlateral radiographic image. By way of example, lateral radiographicimage 358 may be inputted into the system 10. The user may touch thescreen 200 and move lines 360 over at least two points of interest (e.g.the superior endplate of V1 and the inferior endplate of V3) and thesystem 10 then measures the angle between the two lines 360. The Usingthe angle adjustment buttons 328, 330 on the Superior Angle AdjustmentMenu 346 or Inferior Angle Adjustment Menu 348, the user may increase ordecrease the desired angle correction of the spine in the sagittal plane(i.e., add or subtract lordosis or kyphosis superiorly or inferiorly).As either the superior or inferior lumbar lordosis angle is adjusted,the amount of adjustment is dynamically altered in its respective anglemeasurement box (i.e., either superior lumbar lordosis angle box 354 orinferior lumbar lordosis angle box 356). As depicted in FIG. 32, theuser adjusts angle lines 360 as part of the inferior lumbar lordosisangle. The system 10 measures this angle as 20 degrees as depicted inangle measurement field 350. The user then uses button 330 in superiorangle adjustment menu 346 to increase the angle. This change is depictedin inferior lumbar lordosis angle box 356. Once the desired amount ofcorrection is achieved, in this example, it is achieved at 50 degrees.The user may then press the capture angle button 352 and this parametermay be correlated to the digitized screw positions corresponding to thevertebral levels that those angles were measured off of. The system 10may include a color-coded offset distance indicator 322 to provide theuser with an indication of the distance each digitized screw positionwill be adjusted in the sagittal plane as described above. Once thedesired amount of angular correction is achieved, the user may selectthe “Set” button 332, and then the “Calculate Rod” button 272. Thesystem 10 then displays a rod solution 274 incorporating the user'sclinical objective for correction of the spine in the sagittal plane asdepicted in FIG. 33.

It is to be appreciated that, because patient position (e.g., pelvictilt) may have an effect on the lumbar lordosis measurements, thesagittal correction feature of the system will be able to account forany patient positioning-related deviations. It will also be appreciatedthat in addition to lordotic corrections, the sagittal angle assessmenttool may be useful for other types of surgical maneuvers, including butnot limited to pedicle subtraction osteotomy (PSO) procedures andanterior column reconstruction (ACR) procedures.

In some instances, a user may want to align or correct the patient'sspine in the coronal plane (i.e., correct scoliosis). The system 10includes a coronal correction feature in which the user is able persuadeone or more screw locations towards a particular coronal alignmentprofile by manually or automatically biasing which direction the rodbend curve is adjusted. The system 10 then incorporates these inputsinto the bend algorithm such that the rod solution includes the desiredalignment or correction.

Selecting the “Coronal Correction” button 302 from the Advanced Optionsmenu 294 initiates the coronal correction feature. The user may selectat least two points of interest and the system then generates a best fitreference line through all points including and lying between the atleast two points of interest. In some instances, the ideal correction ofthe spine in the coronal plane is a straight vertical line extendingbetween the superior-most and inferior-most screw locations of interest.However, depending on a patient's individual anatomy, achieving astraight vertical line may not be feasible. The user may wish to achievea certain amount of correction relative to the ideal correction. Fromthe display screen, the user may select a percentage of relativecorrection between the screw points as digitized (0% correction) and thebest fit reference line (100%). Furthermore, the system then calculatesa rod solution and shows an off-center indicator 322 to provide a userwith an indication of the distance each screw is from thecoronally-adjusted rod construct as wet forth above.

According to the embodiment shown in FIGS. 34-37, the user maystraighten all points within the construct (global coronal correction).From the display screen 200, the superior and inferior screw points 362,364 are selected and the system 10 generates a best fit global referenceline 366 through all points 362, 364, 368. Using the Coronal CorrectionMenu 370, the user manipulates the + and − buttons 372, 374 to adjustthe percentage of correction desired. In the example shown in FIG. 36,the amount of desired correction is shown as 100% on the percentagecorrection indicator 376, meaning the rod solution 274 will be astraight line in the coronal plane and all screw locations will beadjusted to fit the rod/line. As depicted in FIG. 36, the system 10 mayinclude a color-coded offset distance indicator 322 to provide the userwith an indication of the distance each digitized screw position will beadjusted in the coronal plane as set forth above. If the user deems thisan acceptable rod solution, the user selects the “Calculate Rod” button272 to view the rod solution 274 (FIG. 37) and receive bend instructionsor proceeds to another advanced feature as will be described in greaterdetail below.

According to the embodiment shown in FIGS. 38-40, the user maystraighten a subset of the screw points within the construct (segmentalcoronal correction). Based on the sequence those points are inputtedinto the system, a best-fit segmental reference line is generatedthrough the points in the direction of the last chosen point. If aninferior point 364 is selected first and then a superior point 362 isselected second, the system 10 will draw the best-fit segmentalreference line 378 superiorly as shown in FIG. 38. Conversely, if asuperior point 362 is selected first and then an inferior point 364 isselected second, the system 10 will draw the best-fit segmentalreference line 378 inferiorly. Using the Coronal Correction Menu 370,the user manipulates the + and − buttons 372, 374 to adjust thepercentage of correction desired. In the example shown in FIG. 39, theamount of desired correction is shown as 100% on the percentagecorrection indicator 376, meaning the rod solution 274 will be astraight line in the coronal plane and all selected screw locations willbe adjusted to fit the rod/line. As shown in FIG. 40, however,unselected screw locations 380 will not be adjusted to fit the rod/lineand their relative locations will be inputted into the system 10 andtaken into consideration when the rod calculation is made. As depictedin FIG. 39, the system 10 may include a color-coded offset distanceindicator 322 to provide the user with an indication of the distanceeach digitized screw position will be adjusted in the coronal plane asset forth above. If the user deems this an acceptable rod solution, theuser selects the “Calculate Rod” button 272 to view the rod solution 274(FIG. 40) and receive bend instructions or proceeds to another advancedfeature as will be described in greater detail below.

In some spinal procedures (e.g., anterior column deformity correctionprocedures), restoring a patient's spine to a balanced position may be adesired surgical outcome. The surgical bending system 10 may include aGlobal Spinal Balance feature configured to receive preoperative and/ortheoretical spinal parameter inputs, use these spinal parameter inputsto determine a target rod shape that will restore or improve spinalbalance, display the balanced rod curvature and how that rod wouldtraverse the screws in the deformed spine, and output a target rod thatmay be used to correct the spine to the rod and achieve a desiredbalanced alignment. Depending on user preference, these spinalparameters may comprise Pelvic Incidence (PI), Pelvic Tilt (PT), SacralSlope (SS), Lumbar Lordosis (LL), Superior Lumbar Lordosis (↑ LL),Inferior Lumbar Lordosis (↓LL), C7 Plumb Line offset (C7PL), andThoracic Kyphosis (TK) measurements. The surgical bending system 10 maybe further configured to assess spinal parameter inputs intraoperativelyto determine how the surgical correction is progressing.

FIG. 41 depicts a flowchart indicating the steps of the Global SpinalBalance feature according to one embodiment. At step 390, the system 10inputs a patient's preoperative spinal parameter measurements. Next, thesystem generates theoretical target spinal parameter measurements (step392). One or more target spinal parameter measurements may be optionallyadjusted the user in accordance with a surgical plan a step 394. At step396, a target spinal rod may be scaled to match the patient's anatomyusing the theoretical or adjusted target spinal parameter measurementsfrom step 392 or 394. This scaled target rod may then be displayed 398to the user. Optionally, the system 10 may generate one or moremeasurements (step 400) during the surgical procedure. At step 402, thetarget spinal parameter data may then be adjusted based on theintraoperative measurements from step 400. Finally, the system 10 maygenerate bend instructions for balanced spine correction.

The user may input a patient's preoperative measurements into the system10 as depicted, by way of example in FIG. 42. Selecting the Pre-Opmeasurement button 404 allows the user to input measurements into PI,LL, Superior LL, Inferior LL, C7PL, and TK input fields 408, 410, 412,414, 416, 418, and 420 respectively. These pre-operative anatomicalmeasurements may be used to understand the imbalance in the patient'sdeformed spine as well as help determine an operative plan to implantdevices that would adjust or form the spine to a more natural balance(e.g., rods, screws, a hyperlordotic intervertebral implant, etc.).

As depicted in FIG. 43, the global spinal balance feature allows theuser to adjust the patient's anatomical measurement values to the user'spreferred target spinal parameters for a balanced and/or aligned spine.According to one implementation, selecting the target measurement button406 populates measurements into input fields 410, 412, 414, 416, 418,420 that represent an ideal or properly balanced spine. If the useraccepts these target spinal parameters, the system 10 would output atheoretical rod solution comprising rod shapes and curves representingan ideal or properly balanced spine scaled and overlaid onto thedigitized screw points as shown in FIG. 44. The system 10 may alsoinclude a color-coded offset distance indicator 322 to provide the userwith an indication of the distance each digitized screw position is fromthe rod solution in the sagittal and coronal planes as set forth above.Alternatively, if the user seeks to achieve a different alignment, he orshe may use buttons 422, 424, 426 to adjust these target spinalparameters. The user could then refer to the correction indicator 428for an indication of how much correction (relative to the pre-operativeand theoretical spinal parameters) would be achieved based on thoseadjusted input correction values. The user's input correction valueswould then drive the rod bending algorithm (based on the digitized screwlocations) to a rod shape customized to the user's plan for thatparticular placement. The final rod could be positioned within thepatient and the screws and spine would be adjusted to the rod at thedesired alignment.

In accordance with the Global Spinal Balance feature, spinal parameterinputs may be assessed intraoperatively. For example, the user may wishto intraoperatively measure the amount of lumbar lordosis that has beenachieved (for example, after placement of an intervertebral implant). Asdepicted in FIGS. 45-46, the system 10 may include be configured toobtain or import one or more lateral images, generate one or more linesbetween two or more landmarks on the patient's anatomy, determine arelationship between those landmarks, and adjust one or more spinalparameters to be used in generating the rod solution. As shown by way ofexample in FIG. 45, the user first selects the intraoperativemeasurement button 408. Next, lateral radiographic image 358 may beinputted into the system 10. The user may touch the screen 200 and movelines 360 over at least two points of interest (e.g. the superiorendplate of V1 and the superior endplate of V2) and the system 10 thenmeasures the angle between the two lines 360. As shown in FIG. 45, thesystem 10 measures this angle as 15 degrees as indicated in the anglemeasurement field 350. Optionally, the system may compare theintraoperative measurement to the preoperative and/or target spinalparameter value and provide an indication to the user of how muchcorrection has been achieved relative to the pre-operative andtheoretical spinal parameters. Using the angle measurement buttons 328,330, the user may increase the desired angle of correction of the spinein the sagittal plane (i.e., add or subtract lordosis or kyphosis). Asthe angle is adjusted, the amount of adjustment may dynamicallydisplayed within angle measurement field 350. The system 10 may includea color-coded offset distance indicator (not shown) to provide the userwith an indication of the distance each digitized screw position will beadjusted in the sagittal plane as described above. Once the desiredamount of angular correction is updated, the user may press the “Set”button 332 and then the “Calculate Rod” button (not shown in this view).The system then displays a rod solution 274 incorporating the user'sintraoperative objective for correction of the spine in the sagittalplane.

The user may also wish intraoperatively measure the patient's pelvicincidence angle. As shown in FIG. 47, selecting the intra-op measurementbutton 408 optionally brings up a PI assessment tool. The system 10obtains a fluoroscopic image 452 of the patient's pelvis. The user firstselects the femoral head button 432 and uses arrows 450 on the PIAdjustment Menu 448 to locate the center point of the femoral head 434.Next, the user selects the posterior sacrum button 436 and uses arrows450 to identify the posterior aspect of the sacral endplate 438. Then,the user selects the anterior sacrum button 440 and uses arrows 450 toidentify the anterior aspect of the sacral end plate 442. With all PIinputs selected, the user may press the “Draw PI” button 446 after whichthe system 10 automatically draws and measures the pelvic incidenceangle 446 for the user.

In some circumstances, the user may want to assess the amount/severityof coronal plane decompensation and/or intraoperatively ascertain theamount of correction achieved with a given rod bend configuration. Thesystem may include a Coronal Offset Assessment feature configured toobtain or import one or more Anterior-Posterior images, acquire digitalposition information regarding landmarks on the patient's anatomy,generate one or more lines between those landmarks, and determine arelationship between those landmarks.

According to some implementations, the system 10 first obtains afluoroscopic image 454 of the iliac sacral region (FIG. 48). The userdigitizes two points 456 and selects the Iliac Line: Set button 460 toestablish a horizontal iliac line 458. Next, the user digitizes themidpoint 462 of the sacrum and selects the CSVL Line: Set button 466 andthe system 10 automatically generates an orthogonal line (CSVL line 464)from the sacral midpoint 462 to the iliac line 458. The system 10 thenobtains a fluoroscopic image 468 of the C7 vertebra as depicted in FIG.49. The user digitizes the midpoint 470 of the C7 vertebra and selectsthe “C7PL: Set” button 474 and the system 10 automatically generates anorthogonal line (C7PL line 476) from the midpoint 470 of C7 to the iliacline 458. Finally, the system 10 calculates the coronal offset distance(in box 476) using the offset distance between the CSVL line 464 and theC7PL line 476 line. As such, the user is given an intraoperativeassessment of the amount of coronal offset corrected or left to becorrected which affords the opportunity to decide if a surgical planninggoal has been achieved or if one or more spinal parameter inputs need tobe updated with respect to coronal alignment.

Once the user has selected the desired rod solution, the user thenexecutes the bends using a mechanical rod bender 18. It is contemplatedthat the mechanical rod bender 18 may be any bender that takes intoaccount six degrees of freedom information as it effects bends onto aspinal rod. By way of example, according to one implementation, themechanical rod bender 18 may be the bender described in commonly-ownedU.S. Pat. No. 7,957,831 entitled “System and Device for Designing andForming a Surgical Implant” patented Jun. 7, 2011, the disclosure ofwhich is hereby incorporated by reference as if set forth in itsentirety herein. According to a second implementation, the mechanicalrod bender 18 may be the bender shown in FIG. 50. First and secondlevers 106, 110 are shown as is lever handle 108 designed for grabbingthe lever 106 manually and a base 112 for holding lever 110 in a staticposition. Second lever 110 has a rod pass through 114 so that aninfinitely long rod can be used as well as steady the rod during thebending process with the rod bending device 18. The user grabs handle108 and opens it to bend a particular rod by picking an angle on theangle gauge 132 and closing the handle 108 such that levers 106, 110 arebrought closer together. The mechanical rod bender 18 in otherembodiments could be produced to bend the rod during the handle openingmovement as well. The rod moves through mandrel 118 and in betweenmoving die 120 and fixed die 122. The rod is bent between the two dies120, 122. Gauges on the bender 18 allow the user to manipulate the rodin order to determine bend position, bend angle, and bend rotation. Therod is held in place by collet 126. By sliding slide block 128 alongbase 112, the rod can be moved proximally and distally within themechanical rod bender 18. Position may be measured by click stops 130 atregular intervals along base 112. Each click stop 130 is a measureddistance along the base 112 and thus moving a specific number of clickstops 130 gives one a precise location for the location of a rod bend.

The bend angle is measured by using angle gauge 132. Angle gauge 132 hasratchet teeth 116 spaced at regular intervals. Each ratchet stoprepresents five degrees of bend angle with the particular bend anglegauge 132 as the handle 106 is opened and closed. It is to beappreciated that each ratchet step may represent any suitable degreeincrement (e.g., between 0.25 degrees to 10 degrees). The bend rotationis controlled by collet knob 134. By rotating collet knob 134 eitherclockwise or counterclockwise, the user can set a particular rotationangle. The collet knob 134 is marked with regular interval notches 136but this particular embodiment is continuously turnable and thus hasinfinite settings. Once a user turns knob 134, the user can set the knob134 at a particular marking or in between or the like to determine aparticular angle rotation to a high degree of accuracy. Additionally,base 112 may have a ruler 138 along its length to aid the user inmeasuring a rod intraoperatively.

According to another implementation, the rod bender 18 may be apneumatic or motor-driven device which automatically adjusts thelocation, rotation and bend angle of the rod. By way of example, threemotors may be utilized for each movement. A linear translator motorwould move the rod in and out of the mandrel 118 and moving die 120. Onerotational motor would rotate the rod and moving die 120. The bendcalculations could be converted into an interface program that would runto power and control the motors. The automated bender would lessen thepossibility of user error in following the manual bend instructions. Itwould also increase the resolution or number of bends that can beimparted in the rod making for a smoother looking rod.

Throughout this disclosure, discussion has centered around the abilityto custom bend with specificity a spinal rod during a spinal fixationprocedure utilizing a rod-based spinal fixation construct. An examplemethod for the minimally invasive implantation of such a rod-basedspinal fixation construct 510 will now be described with specificreference to FIG. 51. First, a spinal fixation anchor 512 is anchoredthrough the pedicle of each vertebra to be fixated (e.g. three vertebraas shown in FIG. 51). For the purpose of this disclosure, spinalfixation anchor 512 may be any type of bone anchor capable of receivingand securing a spinal fixation rod thereto (e.g., a bone screw). By wayof example only the spinal fixation anchor 512 includes a rod housing514 for receiving the spinal rod 516 therein and a shank (not shown) foranchoring the housing 514 to the bone. As shown in FIG. 51, each spinalfixation anchor 512 has an extension guide 518 mated thereto for thepurpose of guiding the spinal rod 516 into the rod housing 514. Althoughnot expressly depicted in FIG. 51, it is to be understood that theextension guides 518 provide passage through minimally invasive surgicalopenings in the patient's skin from the outside to the surgical targetsite.

With the fixation anchors 512 in position, a rod 516 appropriately sizedto span the distance between the superior and inferior spinal fixationanchors is selected. The rod 516 may then be prebent or custom-bentaccording to any of the implementations of the disclosure describedabove. In a traditional “open” surgical procedure, a long incision ismade in the patient and the spinal rod is advanced to each screw via theattached guides at essentially the same time through the long incision.Thus, the incision must be at least as long as the rod. During someinsertion techniques the rod 516 is inserted into the guide channel ofthe first fixation anchor 512 generally parallel to the extension guidewhile the insertion instrument is angled back towards the remainder ofthe extension guides 518. As the inserter is rocked towards theinsertion end, the rod 516 advances through each guide.

In a minimally invasive procedure, in contrast, the extension guides 518are placed in a minimally invasive fashion (i.e. through individualopenings without a long incision). As such, an additional opening isneeded either cephalad or caudal to one terminus of the construct. Therod 516 is inserted (via rod inserter 536) through this additionalopening and then sequentially guided (below the skin) through eachsuccessive extension guide 518. Once the rod 516 has been fullypositioned within the guides relative to each of the rod housings 514, arod pusher 520 is advanced along the screw guide and employed to seatthe rod 516 within the rod housing 514. The rod inserter 536 is thendetached from the proximal end 522 of the rod 516 and removed from theadditional opening.

Various examples of rod inserters and rod pushers that may be used (withor without further modification) with the present invention, as well asa more detailed discussion of the surgical technique involved aredisclosed in commonly owned and co-pending U.S. patent application Ser.No. 13/456,210, filed on Apr. 25, 2012 and entitled “Minimally InvasiveSpinal Fixation System & Method,” the entire contents of which is herebyincorporated by reference into this disclosure as if set forth fullyherein.

FIG. 52 illustrates one example of a rod pusher 520 that may be adaptedfor use with the present invention. The rod pusher 520 is used to fullyseat (“reduce”) the spinal rod 516 into the rod housing 514 andthereafter insert a lock screw (not shown) to secure the rod 516 to theanchor 512. The rod pusher 520 may be configured for use with any of therod guide assemblies, for example the extension guides 518 shown herein.Generally, the rod pusher 520 has a proximal end 526, a distal end 528,an elongated central shaft 529 extending longitudinally therebetween.The proximal end 526 may further include a recess 527 configured to matewith an IR tracking array 22 described above. Distal end 528 furtherincludes distal tip 530 for assisting with seating the rod 516 withinanchor 512. Alternatively, the rod pusher 520 may be provided with anintegrated IR tracking array 22 located at the proximal end 526. The rodpusher 520 further includes a handle 532 and a connector 534. The handle532 is located near the proximal end 526 and is configured to allowmanual operation of the rod pusher 520 by the user. The connector 534releasably couples the rod pusher 520 to a guide assembly (for examplethe extension guides 518 described herein).

FIG. 53 illustrates one example of a rod inserter 536 that may beadapted for use with the present invention. By way of example only, therod inserter 536 is an adjustable-angle rod inserter that introduces thespinal rod 516 through the operative corridor at one angle (relative tothe inserter), and then is capable of pivoting the rod at the surgicaltarget site. However, fixed angle rod inserters may also be used withoutdeparting from the scope of the present invention.

By way of example only, the rod inserter 536 includes an outer sleeve538, an inner shaft 540, a handle 542, and a rod holder 544. The outersleeve 538 is an elongated cylindrical member having an inner lumenextending throughout. The inner shaft 540 is an elongated rod memberhaving a proximal end 546 and a distal end (not shown). The proximal end546 includes a knob 548 that is enables a user to employ the variousfunctions of the rod inserter, which are not pertinent to the presentinvention. Further discussion of the rod inserter 536 is available inthe above-referenced '210 application (incorporated by reference). Theproximal end 546 may further include a recess 550 in the top surface ofthe proximal end configured to mate with a IR tracking array 22described above. Alternatively, the rod inserter 536 may be providedwith an integrated IR tracking array 22 located at the proximal end 546.The rod holder 544 is configured to releasably hold the proximal end 522of a spinal rod 516.

Once the fixation anchors 512 have been implanted and the spinal rod 516has been contoured, in some instances the user may want to use thespatial tracking system 12 of the present disclosure to assist with theinsertion and positioning of the spinal rod 516 in the patient. Such usemay make minimally invasive placement of the spinal rod 516 of a longconstruct much easier than currently possible by giving the user a realtime digitized image of the location of the rod tip 524 relative to therod pusher 520 (and implanted anchors 512/guides 518). To facilitatethis, the Advance Options menu 294 discussed above (FIG. 23) may includean additional option to initiate the rod tracking program, for example a“Rod Tracking” option (not shown).

In the instant case, the rod inserter 536 and rod pusher 520 are eachprovided with an attached (or integrated) IR tracking array, such as theIR tracking array 22 shown and described above with reference to FIGS.2-5. Operation of the IR tracking array 22 with regard to the rodinserter and/or rod pusher is essentially the same as the operation ofthe IR tracking array 22 with the digitizer pointer 30 described above.

The user selects the “Rod Tracking” button from the Advance Options menu294 that navigates the user to a Rod Tracking screen as depicted inFIGS. 54 and 55. The proximal end of the contoured rod 516 is attachedto the rod holder 544 of the rod inserter 536 (with IR tracking array).To calibrate the system 110, the user inserts the distal tip 524 of thespinal rod 516 into a calibration aperture 550 located on the distal end528 of the rod pusher 520 and then presses the “Calibrate Rod” button556 on the GUI. This calibration step calculates the distance andorientation of the rod inserter handle 542 to the rod pusher 520.

The user then inserts the rod pusher 520 (with attached or integrated IRtracking array) into the first targeted extension guide 518 (i.e. theextension guide that this closest to the additional skin opening) anddigitizes the screw via the process described above. As shown in FIG.54, at this point the GUI then shows a graphic representation of thetargeted screw head 552 (e.g. depicted as a static sphere, detailedtulip, and the like) in both the sagittal and coronal views. The userthen inserts the rod 516 though the additional opening and advances ittoward the first targeted extension guide 518. As the distal tip 524 ofthe rod 516 approaches the target extension guide 518, the GUI shows adynamic graphical representation of the distal tip 554 in both distanceand direction/orientation relative to the target extension guide 518.Using this information, the user can then manipulate the rod inserter536 to accurately guide the distal tip 524 of the rod 516 to thetargeted screw, by guiding the graphical representation of the rod tip554 to the graphical representation of the screw head 552 on the GUI, asshown in FIG. 55. Once the distal tip 524 of the rod 526 is successfullypositioned within the first extension guide 518, the rod pusher 520 isremoved (or a second rod pusher 520 with IR tracking is used) andinserted into the extension guide 518 for the second targeted screw.This second location is then digitized using the process describedabove. The user then continues to advance the distal tip 524 of the rod516 toward and through the second targeted extension guide 518. Thisprocess continues until the entire rod 516 is properly positioned withinthe extension guides 518.

Once the rod 516 is properly positioned within the extension guides 518,the rod holder 544 of the rod inserter 536 is detached from the proximalend 522 of the rod 516 and the rod inserter 536 removed from theadditional opening, which can then be closed. One or more rod pushers520 are employed to seat and secure the rod 516 within the rod housing514 of the screw head, and the pusher 520 and extension guides 518 areremoved from the operative corridor(s) before closing the operativewounds.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown, by wayof example only, in the drawings and are herein described in detail. Itshould be understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed. On the contrary, the invention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined herein.

What is claimed is:
 1. A method for correcting the curvature of a spineof a patient, comprising the steps of: implanting a plurality of bonescrews at various locations along a spine, each of the plurality of bonescrews having an anchor portion and a rod housing, the anchor portionadapted to provide purchase within bone and the rod housing configuredto receive at least a portion of a spinal rod therein; digitizing thelocations of said plurality of implanted screws using a digitizingpointer comprised of a housing having shutters manually operable betweenan open position and a closed position, whereby said shutters exposereflective markers attached to said housing in the open position uponsqueezing a handle of said housing, and whereby a digitizing pointersensor detects said locations of said plurality of implanted screws whenthe shutters are in the open position; digitizing a distal end of aspinal rod attached to a rod inserter that enables the spinal rod toadvance through an operative corridor; seating, with a rod pusher, thespinal rod in at least one of said rod housings; wherein at least one ofthe rod inserter and the rod pusher has an emitting component thereonthat can be sensed by a sensor; continuously generating a dynamic visualoutput on a graphic user interface corresponding to the relativelocations of the digitized screws and the digitized distal end; andadvancing the distal end of the spinal rod through the operativecorridor toward a first of the implanted screws while receiving thedynamic visual output on the graphic user interface.
 2. The method ofclaim 1, wherein each implanted screw has an extension guide removeablyattached to the rod housing, the extension guide adapted to transientlyreceive at least a portion of the spinal rod therein, the extensionguide further adapted to receive at least a portion of the rod pusher.3. The method of claim 2, wherein the rod pusher is adapted to mate withthe extension guide, the rod pusher having at least one rod engagingsurface adapted to contact the spinal rod.
 4. The method of claim 3,further comprising the step of calibrating a distal end of the rodpusher with the distal end of the spinal rod.
 5. The method of claim 4,further comprising the step of advancing the rod pusher along theextension guide until the at least one rod engaging surface ispositioned near the rod housing.
 6. The method of claim 5, furthercomprising the step of advancing the distal end of the spinal rodthrough the extension guide removeably attached to the first implantedbone screw.
 7. The method of claim 6, further comprising the step ofadvancing a second rod pusher along a second extension guide, the secondextension guide removeably attached to a second implanted bone screw. 8.The method of claim 7, further comprising the step of advancing thedistal end of the spinal rod toward the second extension guideremoveably attached to the second implanted bone screw.
 9. The method ofclaim 8, further comprising the step of advancing the distal end of thespinal rod through the second extension guide removeably attached to thesecond implanted bone screw.
 10. The method of claim 9, furthercomprising the steps of: advancing the first rod pusher along the firstextension guide until the at least one rod engaging surface contacts theportion of the spinal rod present within the rod housing; securing thespinal rod within the first rod housing; advancing the second rod pusheralong the second extension guide until the at least one rod engagingsurface contacts the portion of the spinal rod present within the secondrod housing; and securing the spinal rod within the second rod housing.